2012 ford expedition Ltd p0303 misfire cylinder 3
 

Hi, I hope I'm in the right area I am new here. I purchased a 2012 Ford expedition Ltd in December with 116k miles. Drove it 2 hours home from the dealership the the next day 3.5 hours for holiday vacation and on the way the cel came on. The code showed the p0303. Local shop changed the spark plug. He was surprised they had new Bosch vs Motorcraft. Took it home and next day cel again. Same code. There is a shake upon startup and rough idle. I can also smell exhaust. Took it back and they checked coils fuel injectors did a compression test and advised they think it's the heads leaking. This is alot of money and I called the dealership as I had only had it less than 3 days. After about 2 weeks in which it sat at my shop (they also replaced the 3 coil) they agreed to come get it and repair. (2hours away)Their Ford dealership had it and said it was the fuel injector...replaced and said it was fixed. I was confused as this had already been tested but what do I know. They had it 2 months...came home on Friday and Saturday I noticed a rough idle slightly. By Monday it was pretty rough again and low and behold cel and same code. I called dealership back and they are suppose to let me know next steps. I'm at a loss? This p0303 code is crazy. I still feel like it would be the head vs all the other items. Has anyone else seen this issue? It's the 5.4 triton. Thank you in advance.

Maybe your description is not quite complete, but it seems like the "Guessing game" is in full swing.
The guessing game goes like this, lets replace this , maybe that is the problem. If not, then lets replace that and so on.
What somebody needs to do is , know exactly what is happening, how the system actually works then verify if the desired result is obtained. From your description, that does not appear to be getting done, . Just because you took it to a dealership, if they gave the problem to someone that is there for a paycheck only, find a better dealership.or shop.

You are correct it's a guessing game. Where the problem comes in however is the estimate I got from my local mechanic is over 4k to work on the heads. I don't have that kind of money, nor am I mechanically inclined. It was taken back to the dealership where it was purchased because they said they would fix it. So for now I'm am at the mercy of the people agreeing to try to solve the problem. I am just trying to understand for myself what could be causing that p0303

The replacing of the spark plug and coil, hopefully, should eliminate those possibilities.
Can you help us out some,
what are you doing with the vehicle when the misfire takes place?
Does it misfire right at start up?
Does the engine need to warm up before it starts to misfire ?
If it only begins after you start driving for a while, how long and how fast is the vehicle going.
There is a function called "Freeze Frame". The vehicle computer will record the data stream at the time the misfire takes place and the conditions .
A repair person should look at this info since it will provide the circumstances when the problem appeared and the check engine light came on.
A capable tech will usually spot when something is different from normal and that can provide a clue/path to where the problem might be originating.
Dealerships have the equip to do all this and it puzzles me why they could not come up with the root cause.
Maybe they had some idea of the problem and ,,,,,,,,,and ,well who knows. We don't second guess, but we do wonder sometimes.
As long as the dealership is covering the cost of repair, not much choice, be patient, yet persistent !

Hi , that was kind of my concern is that this was known before I got it. :( I'd like to believe the best in people but find it hard to believe this randomly happened less than 3 days after and still won't go away. It happens upon start up. It's loud and rough idle and then as im driving it seems to calm down but when I'm sitting at a stop light for instance or sitting in park I can feel that light shaking. My local mechanic started with the most common he said which was the plugs and coil, he also did some switching of them around I guess to see if it followed or stayed with cylinder 3 and it did. He did the compression test and said that was also fine and checked the injectors and ran engine cleaner through twice which then led him to believe it was the head leaking. (He replaced spark plug first visit and cel came on very next day) second visit is when he did everything else. The dealership of course did not want to pay for him to fix they wanted it back to them. So they towed it and their shop (which is not a Ford dealership but a large well known one) wanted an actual Ford affiliated mechanic to look at it before they dug into the engine. I let them know and gave them all the local mechanics findings but they still said fuel injectors. After it was "fixed" I ask that they keep it a few days and drive it just to be safe..and they said they did., but here we are. I love the vehicle it's pristine and miles for a 2012 not bad but now I'm afraid I was had...:(

A compression test at low cranking speed may not show up a broken valve spring that shows up with higher RPM. This would require removing the passenger side valve cover to confirm.

Did your mechanic say what the plug for # 3 cylinder looked like? If coolant is getting in there the plug will show that and the exhaust will produce an anti-freeeze "fragrance"..

If a head gasket were a possible cause compression would be getting into the cooling system and pressure will force coolant out the overflow bottle.

Hopefully a tech with a little more background will be assigned the lob, and he/she should be able to find it pretty quick.

A good tech with a scope should be able to spot a problem involving combustion.

Do we know if the Powertrain computer was confirmed operating correctly for that cyl?